The valve bodies of internal combustion engine valves are typically subjected to elevated temperatures and corrosive action as a result of exposure to exhaust and combustion gases and generally experience considerable wear on their seating surfaces. For these reasons, the valve bodies are formed of durable alloys, such as stainless steel, and are provided with corrosion- and wear-resistant properties either by special treatment of the seating surfaces or by "armoring", "cladding" or "facing" the seat-forming portion with heat-, wear- and corrosion-resistant materials, frequently referred to as hardfacing materials. It is, therefore, common practice, particularly in the manufacture of exhaust valves to hardface the valve on its frustoconical seating surfaces with a corrosion and abrasion resistant alloy to protect the valve face and enhance the durability of the valve. In a typical case, the valve body is formed of an austenitic or martensitic steel or a nickel-chromium base alloy and the facing material is a nickel-chromium, nickel-chromium-cobalt or cobalt-chromium-tungsten base alloy, such as one of the Stellite alloys.
The hardfacing material is typically applied to the valve seating surface by various high temperature techniques, such as by depositing the material in a liquid state and fusing it to the surface or by applying the material in the form of a preformed ring and bonding it to the surface by techniques such as plasma arc or oxyacetylene gas or shielded arc electric welding. According to one particularly desirable method for applying a corrosion- and wear-resistant alloy to the seating surface of an exhaust valve, the frustoconical seating surface is first channeled, fluted, grooved or otherwise formed with a shallow annular recess or depression and the hardfacing alloy is placed or deposited therein for bonding to the groove surfaces by one of the aforementioned techniques or any other suitable metal deposition technique.
It has been found that at the very high temperatures used during oxyacetylene or other bonding of the hardfacing alloy to the groove surfaces, and particularly at the high temperatures experienced using plasma arc techniques, there occurs an undesirable melting of the valve body in the areas radially inward of and adjacent to the groove formed in the seating surface of the valve body. This melting of the valve body causes and encourages the valve body material to diffuse into and dilute the hardfacing alloy composition adjacent the melted areas. The diluted hardfacing material exhibits a notable deterioration in corrosion and wear resistance which adversely affects the ability of the material to perform its intended function.
It is therefore the purpose of the present invention to overcome this previously encountered material dilution problem, to provide an improved method of hardfacing the seating surfaces of internal combustion engine valves with wear- and corrosion-resistant alloys and to provide an improved valve for internal combustion engines having wear- and corrosion-resistant seating surfaces.